(1) Field of the Invention
This invention relates to an apparatus and method for sputter cleaning and more specifically to an apparatus and method for sputter cleaning wherein the temperature of the pedestal on which a substrate to be cleaned is placed is controlled by flowing cooling liquid through the pedestal.
(2) Description of the Related Art
In a conventional sputter cleaning system a wafer, or other substrate, is placed on a layer of insulating material formed over a pedestal formed of conducting metal. FIG. 1 shows a top view and FIG. 2 a cross section view of a conventional wafer and pedestal arrangement. FIG. 2 shows a pedestal 10 having a layer of first insulating material 14 formed thereon. A layer of second insulating material 12 is formed on the sidewall and bottom of the pedestal 10. A wafer 16, or other substrate to be sputter cleaned, is placed on the layer of first insulating material 14. Silicon pins 32 extend through the second insulator 12 into the pedestal 14 to act as a radio frequency power antenna. Substrate extraction holes 42 provide for rods to be inserted to remove the substrate 16 after the cleaning has been completed. FIG. 1 shows the top view of the pedestal and wafer arrangement. The cross section view shown in FIG. 2 is taken along line 2-2xe2x80x2 of FIG. 1.
The wafer 16, shown in FIGS. 1 and 2, is insulated from the metal pedestal 10 by the layer of first insulating material 14 and the pedestal 10 is insulated by the second insulator 12 so that during sputter cleaning of the wafer 16 the wafer temperature can become very high. This elevated wafer temperature has undesirable effects for later processing steps.
U.S. Pat. No. 6,077,353 to Al-Sharif et al. describes a pedestal insulator for a pre-clean chamber.
U.S. Pat. No. 6,033,482 to Parkhe describes a method for lighting a plasma in a plasma processing chamber, showing a plasma chamber with a pedestal.
U.S. Pat. No. 6,081,414 to Flanigan et al. describes apparatus for biasing and retaining a workpiece in a processing system. The apparatus includes a pedestal, a puck, and an electrode between the pedestal and the puck. The puck is an electrostatic chuck to hold the workpiece. The electrode can serve as a cooling plate for the puck.
U.S. Pat. No. 6,090,246 to Leiphart describes methods and apparatus for detecting neutral gas molecules reflected from a target during sputter deposition. Leiphart describes, but does not show, a cooling device, such as a water cooled backing plate to cool the target material during the sputtering process.
U.S. Pat. No. 6,077,404 to Wang et al. describes a method and apparatus for reflowing a material layer.
In a sputter cleaning system a pedestal 10, formed of conductive metal, forms a conductive surface below the wafer 16 so that the sputter cleaning can be accomplished, see FIG. 2. The wafer 16 is insulated from the conductive pedestal 10 by a layer of first insulating material 16, see FIG. 2. In this arrangement the temperature of the pedestal and wafer rise with continued cleaning because there is no path to remove the heat energy from the pedestal and wafer. This temperature rise can cause processing problems. Specifically in deposition of a layer of Ti/Al/TiN excessive temperature during cleaning will promote the formation of TiAl3 which can result in void formation in the structure.
It is a principle objective of this invention to provide a method of sputter cleaning a substrate, such as a wafer, where the pedestal is cooled and the temperature of the pedestal is controlled.
It is another principle objective of this invention to provide an apparatus for cooling the pedestal and controlling the temperature of the pedestal during sputter cleaning of a substrate, such as a wafer.
These objective are achieved by forming a cooling channel in the metal pedestal. The cooling channel is made up of pipes for flowing cooling liquid, such as water. Any form of pipes can be used such as concentric, radial, or other appropriate shape for directing the cooling liquid. An inlet tube delivers a cooling liquid, such as water, to the cooling channel and an exhaust tube removes the cooling liquid from the cooling channel thereby removing heat from the pedestal.